Background: This study aimed to explore the potential causal relationship between frailty and allergic diseases through bidirectional Mendelian randomization (MR) analysis.

Methods: Single nucleotide polymorphisms (SNPs) were selected as instrumental variables from genome-wide association studies summary data. The inverse variance weighted (IVW) method was used as the main analysis method, and MR-Egger regression and weighted median method were employed to complement the IVW results. Verification of the reliability of results using multiple sensitivity analysis methods.

Results: The results of forward MR analysis revealed a statistically significant positive causal relationship between allergic asthma (AA) and frailty, as well as between atopic dermatitis (AD) and frailty; however, no causal effects were detected between allergic conjunctivitis (AC), allergic rhinitis (AR) and frailty. The results of reverse MR analysis indicated that frailty had a statistically significant positive causal effect with AD and AR, but no causal effect with AA or AC. The sensitivity analysis showed that the MR results were stable, with no heterogeneity and horizontal pleiotropy.

Conclusions: This study found a bidirectional causal relationship between AD and frailty, a positive causal relationship between AA and frailty, an inverse causal relationship between AR and frailty, and no causal relationship between AC and frailty. In view of this, it may be recommended to promote routine frailty screening among patients with AD and AR to help identify high-risk individuals early. Additionally, appropriate interventions for frailty are crucial to reduce the risk of AA and AD.